Hmmm, there's something about the lighting. You said you increased the occlusion weight. That's noticeable. But for some reason the shadows still look unnaturally bright. It seems you checked "soft shadows", didn't you? That's better, but the soft lighting cast by some overcast sky doesn't really fit to the shadows that are quite sharp near the shadow emitter.
If you wouldn't have written, that there is no additional lightsource I would have bet there is one. Strange...
